Harbinger Trouble - Lamp Not Pulsing - Problem Solved

[mshuptar]

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Hey y'all,

I built the Harbinger in summer of 2014 and I've absolutely loved it. A few months ago, the effect stopped working.
It was like the effect got weaker and weaker. The pulsing didn't seem as deep, and eventually, it just stopped.

There's a signal in bypass mode, and there's a signal when the effect is engaged. I opened up the unit and saw that the mini lightbulb wasn't blinking anymore although the rate LED still blinks.

Here's what I've done so far:
1) Reflowed all the joints and connections (and double checked the connection at the speed pot)
2) Got out my meter and took measurements (see results below)
3) I remember reading on another troubleshooting thread to check Q11-13. When I checked values with my meter, I didn't get readings too far outside the range printed on the build doc. (I replaced them anyway to see if it made a difference; it didn't.) 

Here's what I haven't tried:
1) Throwing the PCB against the wall
2) Hitting it with a hammer
3) Getting a new Speed pot.






Any thoughts?

[Axeman]

Can you post a pic of the dual pot

[mshuptar]

No prob:

[mshuptar]

Update 12/10. I've been following Axeman's troubleshooting feed here: http://www.madbeanpedals.com/forum/index.php?topic=24161.0 , and I've been trying to problem solve on my own.

The rate LED still blinks, but the lamp does not. Thinking that transistors Q11-13 might be the problem, I swapped them out and put in new ones. This did not solve the issue. Is there a way to check if the rate pot is bad?

I'm a little puzzled because I gigged heavily with this pedal on my board since the summer of 2014.

[mshuptar]

3/31:

I swapped out the Speed pot and the lamp still doesn't blink. It lights up when plugged in, but the lamp doesn't blink. Any thoughts? What could I be missing?

[mshuptar]

4/5: I spent an hour reading about the Univibe circuit on R.G. Keen's site. I didn't totally comprehend everything, but I was able to figure out that there must be a problem in the LFO / Lamp driver section. I got out the audio probe and found that R46 had gone bad.  Once I replaced it, the lamp started pulsing again. Awesome!

Random question: what would cause a resistor to go bad? Has anyone had this happen in the Harbinger before?

[midwayfair]

4/5: I spent an hour reading about the Univibe circuit on R.G. Keen's site. I didn't totally comprehend everything, but I was able to figure out that there must be a problem in the LFO / Lamp driver section. I got out the audio probe and found that R46 had gone bad.  Once I replaced it, the lamp started pulsing again. Awesome!

Random question: what would cause a resistor to go bad? Has anyone had this happen in the Harbinger before?

If the resistor was mismarked or out of spec, it might have just be wrong in the first place.

A resistor "going bad" usually means that it actually burns up -- too much current is drawn through it, and when it tries to dissipate the heat, the amount of heat it dissipates exceeds the wattage rating of the resistor, and it literally goes up in smoke. You would know if this happened.

[bluescage]

Glad you solved the problem!

[Axeman]

Awesome